1. Field of the Invention
The present invention relates, in general, to a harmonic quadrature demodulation apparatus and method used for an ultrasound harmonic imaging scheme, and, more particularly, to a harmonic quadrature demodulation apparatus and method, which eliminate a fundamental frequency component from an externally received focused signal, and extracts only a second-order harmonic component from the focused signal.
2. Description of the Related Art
Harmonic imaging is a technique for extracting only harmonic components from a received signal and imaging the harmonic components. Since this harmonic imaging has better resolution than a method using a fundamental frequency, it is widely used to image a contrast agent or the characteristics of tissue. Harmonic imaging methods that are most frequently used may include a method using a band pass filter and a pulse inversion method.
Such a method using a band pass filter is a method of extracting harmonic components from an input focused signal using a band pass filter, and is problematic in that the bandwidth of a transmission signal is limited to prevent the spectrums of a fundamental frequency component and harmonic components from overlapping each other.
Further, a pulse inversion method is a method of performing two transmission/reception procedures using two transmission pulses having a phase difference of 180 degrees therebetween, thus eliminating a fundamental frequency component and retaining only harmonic components. In the case of this method, the bandwidth of a transmission signal is not limited, but there is a disadvantage in that, since transmission/reception must be performed twice, the frame rate is decreased to half that of the case where transmission/reception is performed once.
Accordingly, the present applicant intends to propose a scheme capable of overcoming the disadvantage of the pulse inversion method, and extracting harmonic components through only a single transmission/reception procedure without limiting the bandwidth of a transmission signal.